1. Write a definition of "diffusion".
Answer
Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
2. Which plant organ is not adapted for exchanging materials with the environment ?
a) roots b) stem c) leaves d) flowers
Answer
d) flowers
3. Write out the equation for calculating percentage change in mass.
Answer
% change in mass = (change in mass ÷ starting mass) × 100
4. Which process do plants use to take up mineral ions from very dilute solutions ?
a) Diffusion b) Osmosis c) Active transport d) Photosynthesis
Answer
c) Active transport
5. Explain how single-celled organisms obtain the oxygen they need for aerobic respiration.
Answer
Their large surface area to volume ratio allows oxygen to diffuse efficiently into the cells through the cell membrane.
6. Substances may move into and out of the cells of living organisms by diffusion. Name the factors that affect the rate of diffusion.
a) The presence of chlorophyll and the amount of sunlight
b) The colour of the cell and the type of tissue
c) The number of chromosomes and the size of the nucleus
d) Temperature and the surface area of the membrane
Answer
d) Temperature and the surface area of the membrane
7. The small intestine of mammals is adapted to absorb digested food. The small intestine contains finger-like projections called villi. The figure below shows one villus. Explain some ways that the small intestine is adapted for its function.
Answer
Walls of villi are only one cell thick so short diffusion path. Network of capillaries (or rich blood supply), so steep concentration gradient. Millions of villi so large surface area.
8. A student investigates osmosis by measuring the effect of different concentrations of salt solution on the mass of carrot cylinders. What is the independent variable for this investigation ? What is the dependent variable ?
Answer
Concentration of salt solution is the independent variable. Change in mass of carrot cylinders is the dependent variable.
9. Describe two differences between active transport and osmosis.
Answer
Active transport requires energy from respiration and moves substances against a concentration gradient.
10. Some soils are water-logged. This means that there is water filling the air spaces in the soil. Explain why plants grown in water-logged soil are deficient in mineral ions.
Answer
There is less oxygen available, resulting in reduced aerobic respiration and consequently less energy for active transport.